I usually go this way at park open, and honestly you may not need that BTMRR FP at that time. I've done JC, POTC, BTMRR x2, and Splash all with practically no waits at that time of the morning. The line for BTMRR is building after the first ride, but not that quickly. Of course, it does burn one so you can try for more later. I'm the type who usually schedules my FP a bit later.